i want to get call of duty modern warefare2 for my bday and i was wondering will my pc lag when i play it this is my setup psu:300watt cpu:athlon am2 3500+ gpunboard 512mb geforce 8100 ram:3gigs of samsung 800mhz ddr2.Would i need to oc my cpu or gpu O and my mobo is ecs gf8100vmm5 i bought this as it is very good for the money

CODMW2 is a graphics intensive game that can put some of the best machines to shame. Like the others above me stated, it will play alright on low. I don't know what kind of motherboard you have but if its something decent then a CPU upgrade might do the trick. If you have a PCI-E slot then a GPU upgrade would be feasible too. . but I would do this first, before the CPU. If you are using AGP on your MOBO then maybe its time to get a "barebones" system (motherboard/cpu/case/) and throw in your other components to have a really nice system.

Other than that, it depends on the quality level you want to play the game on. If you are satisfied with low/med-low , then yeah you should be fine, but if you want to play on HIGH, then you will def. need an upgrade.